The present invention relates generally to a method by which the heat transfer quality of a cooled gas turbine engine component can be quantified for inspection purposes. More particularly, in one embodiment the present invention determines the heat transfer performance of an internally cooled structure by analyzing the transient thermal response of the structure based upon a full field surface temperature measurement using an infrared thermal imaging system. Although the present invention was developed for use in association with gas turbine engine components, certain applications may be outside of this field.
A gas turbine engine conventionally comprises a compressor for compressing air to the proper pressure required for supporting the combustion of fuel in a combustion chamber. The high temperature gas exiting the combustion chamber provides the working fluid for the turbine, which powers the compressor. The turbine, which is driven by the flow of high temperature gas, is utilized to turn a propeller, fan or other device. Further, the high temperature gas may be used directly as a thrust for providing motive power, such as in a turbine jet engine.
It is well known that the performance of a gas turbine engine increases with the increase in the operating temperature of the high temperature gas exiting the combustion chamber. A factor limiting the allowable temperature of the gaseous working flow from the combustion chamber is the capability of the various engine components to not degrade when exposed to the high temperature gas flow. Engine designers to cool the engine components in order to increase the upper limit on the operating temperature of the gaseous working fluid have utilized various techniques. A conventional technique that engine designers have used to allow the use of higher temperature working gases is an internal network of apertures and passageways within the component. A steady flow of pressurized cooling media is passed through the internal passageways of the component, and the cooling media is finally exhausted onto the exterior surface of the component. The passage of the cooling media through the internal passageways and out through the exit aperture provides for convective heat transfer from the walls of the component to the cooling media.
Cooling of the components of the gas turbine engine is preferably accomplished with a minimum amount of cooling media, since the cooling media is working fluid, which has been extracted from the compressor, and its loss from the gas flow rapidly reduces engine efficiency. The engine designer must design an engine to operate within a specified temperature range, while minimizing the amount of cooling media extracted from the compressor. If these design parameters are not satisfied, a corresponding structural degradation of the engine components may result, or the efficiency of the engine may be reduced because an excessive quantity of cooling media was extracted from the compressor.
Over the years, a number of techniques have been developed to inspect the cooling quality of gas turbine components. These techniques include (1) total, regional, or hole-by-hole airflow measurement; (2) water flow visualization; (3) ammonia/blueprint paper; and, (4) various less sophisticated thermal imaging techniques. The prior techniques are not able to detect internal flow characteristics and/or internal flow anomalies. Further, technique (1) is time consuming and techniques (2)-(4) are non-quantitative in nature.
Although the prior techniques are steps in the right direction for inspecting the cooling quality of gas turbine components exposed to high temperature gases, the need for additional improvement still remains. The present invention satisfies this need in a novel and unobvious way.
One form of the present invention is a technique to evaluate thermal response of an internally cooled structure. This technique includes determining one or more heat transfer characteristics of the structure.
In a further form of the present invention, evaluation data is provided by observing temperature changes over time at each of a number of locations along a structure. The evaluation data corresponds to a convective heat transfer coefficient estimated for each of the locations. The evaluation data may be used to assess the quality of parts by comparing the data to a known standard, to analyze initial thermal behavior of a new device configuration, or to direct repairs or maintenance, to name just a few applications.
In another form of the present invention, data is obtained by an infrared thermal imaging system observing temperature changes over time at each of a number of locations along the surface of a component that is being tested at near ambient conditions. The data is processed to separate the heat transfer associated with convection from conduction for the component at near ambient conditions.
One object of the present invention is to provide a unique method for determining the heat transfer performance for an internally cooled structure.
Related objects and advantages of the present invention will be apparent from the following description.